We plan to develop and characterize a new experimental model of iron overlaod to determine the role of iron in the pathogenesis of liver injury. We will use a system in which dietary iron overload in the rat leads to excessive intestinal iron absorption and subsequent preferential deposition of storage iron in the parenchymal cells of the liver,. Our initial studies have shown that supplementation of the diet with 2.5% carbonyl iron (highly purified elemental iron in very small particulate form) produces hepatic iron concentrations of up to 5000 Mug/g within 5 weeks and over 10,000 Mug/g in 6 months (normal controls less than 200 Mug/g). This is deposited as ferritin and hemosiderin in lysosomes and cytosol, and is associated with spotty hepatocellular necrosis and ultrastructural evidence of increased collagen formation. In our proposed studies we will investigate in detail the consequences to cell structure and function of heavier and more prolonged iron overload. In the course of development of iron overload we will evaluate the metabolism of carbonyl iron in terms of intestinal absorption, and tissue uptake, storage and release. We will assess the functional role of storage iron in the regulation of hepatic transferrin and ferritin metabolism in the isolated perfused liver. We will correlate the biochemical and ultrastructural characteristics of storage iron with certain identifiable cytopathological events in the liver. One such major cytopathic event has already been observed after relatively short term iron overlaod. We have made the first direct identification of lipid peroxidation in vivo in microsomal and mixed mitochrondrial/lysosomal fractions of liver from rats with iron overload. The potential effects of lipid peroxidation on the structural and functional integrity of microsomes, mitochondria and lysosomes will now be assessed with specific biochemical and ultrastructural markers. We will correlate observed changes with the degree of iron overload, the form and localization of intracellular iron and the extent of lipid peroxidation in vivo. Finally, we will assess fibrogenesis in chronically iron overloaded liver by measuring net collagen synthesis. By exploiting this new model we hope to gain insight into the pathogenesis of liver damage in hemochromatosis though an integrated series of morphologic, metabolic and biochemical observations carried out under controlled, measurable conditions.